The present invention relates to a current supply device for electrically heating a molten medium, or melt, which is disposed in a melting trough, by means of in-phase alternating currents which are fed into the melt via one or a plurality of secondary windings of one or a plurality of individual transformers and which penetrate the melt through electrodes and counterelectrodes immersed therein.
Such current supply devices can be used for heating molten media of the kind that offer an ohmic resistance to the heating current and thus constitute a resistive load. Such devices are used, for example, in glass and salt melts.
The molten medium disposed in a melting trough receives its heating current from an a.c. current source via a transformer or a plurality of individual transformers having a plurality of secondary windings and further via electrodes which are immersed in the medium, and the current is removed from the medium via counterelectrodes which are likewise immersed therein. The electrode arrangement causes the heating current to be divided into a number of component alternating currents corresponding to the number of electrode and counterelectrode pairs and distributed in cross section through the molten medium.
The current supply devices employed must assure that the electrodes and counterelectrodes receive current loads which are as identical as possible so that in operation they are consumed at the same rate and thus all participating electrodes have as nearly as possible the same service life.
However, attainment of identical current loads on the electrodes is difficult since the distribution of the component alternating currents is nonuniform and fluctuates due to differences and changes of local conditions in a melt. In current supply devices in such use, the component alternating currents are electrogalvanically separated from one another, and are each fed from one secondary winding of a transformer, as mentioned above, or are fed from individual transformers. In these devices a static alternating current switch is connected ahead of every individual transformer so that it is possible to individually set the component alternating currents, but the costs involved become considerable as do the difficulties in regulation due to the mutual influence between the individual currents and current paths.
Finally there are electrodes and counterelectrodes which are arranged in pairs spatially offset with respect to one another, each connected to a secondary winding of a transformer having a common primary winding or to a respective individual transformer, in which case a plurality of current paths or the current paths of a pair of component currents may intersect so that differences between component alternating currents due to local conditions in the melt are reduced.
All of the above-described measures taken to provide current loads which are as identical as possible on the electrodes are still not fully sufficient for this purpose.